The Night Sky This Month: October 2016

In the early evening, the bright red supergiant star of Arcturus in Bootes presents a beautiful sight in the western sky, while a little later the star fields associated with Sagittarius and Scorpius will also provide a fine target for astronomers. In the meantime, the constellations of Pisces and Cetus will rise a little after nightfall in the east, followed later by the Great Square of Pegasus, and in the early hours the Pleiades and Orion.

As always, circumpolar constellations including Cassiopeia, Ursa Minor, and Ursa Major can be viewed in the northern celestial heavens, although the Plough of Ursa Major is beginning to near its autumnal low-point below Polaris. To their west can be seen the stars which form the Summer Triangle, namely Deneb (Cygnus), Vega (Lyra) and Altair (Aquila).

The Moon & Phases

Folklore has it that the first full Moon after the September Harvest Moon should be known as the Hunter’s Moon, probably because the full Moon on the 16th of the month is high in the sky, thus providing better light for poachers to practice their craft. Whatever the origin of the name though, it is rather apt, since the Moon will be “stalking” several stars in the Hyades cluster, eventually occulting them on the night of October 18th/19th on its way toward the star Aldebaran in the constellation Taurus.

The Moon will also be at apogee (406,096 km) on both October 4th and October 30th (406,662 km), and at perigee (357,861 km) on the 17th of the month, representing a difference of 48,000+ km in the angular diameter of the Moon as seen from earth.

– The Orionids meteor shower is produced by debris left behind by Halley’s Comet, and this year, Earth will encounter the debris trail between October 21st, and October 24th. A maximum hourly rate of between 20 and 25 meteors is expected from a radiant just to the north east of the star Betelgeuse in the constellation Orion. The Orionids often produce fast meteors, many of which are expected to leave smoke trails in their wake.

– The Draconids is generally regarded as a minor shower that rarely produces more than 10 meteors per hour. This year, the peak is expected to occur on October 8th from a radiant in the constellation Draco, the Dragon. This shower is associated with the comet Giacobini-Zinner, hence its alternative designation, the Giacobinid shower.

The Planets

– Mercury is in its best morning apparition for 2016, and it can be seen shining brightly low above the eastern horizon until the 11th of the month. After this date, the little planet approaches a position of superior conjunction with the Sun, and it will therefore not be visible. However, before it disappears it will form a pretty duo with Jupiter against the background stars in Virgo during the first two weeks or so of October. On the 11th of the month, Mercury will be about 0.75 degree above Jupiter, but the pairs low elevation (10 degrees) above the eastern horizon might make the pairing difficult to spot.

– Venus is difficult to spot during October, rising barely six degrees above the horizon in the southwest. Moreover, at the start of the month it sets only 50 minutes or so after the Sun, which then increases to 90 minutes by the month’s end. Nonetheless, for observers under dark skies, it might be possible to track Venus as it moves eastward from Libra towards Scorpius, and then on to Ophiuchus, where it will form a close pairing with Saturn by month’s end.

– Mars starts October by setting about three hours after the Sun, before increasing to about four and a half hours by month’s end, because its elevation above the horizon increases sharply as it traverses the constellation Sagittarius on its way toward Capricornus. Look for Mars as it traverses Sagittarius almost clipping the star Kaus Borealis, the “filial” at the top the Teapot asterism on the 7th of the month. Even though the red planet dims somewhat during the month, it remains the brightest object low on the southwestern horizon below the star Altair in the constellation Aquila.

– Jupiter is now in the constellation Virgo, shining at magnitude -1.7, and is becoming more prominent as a predawn object as the month wears on. Look for Jupiter about two degrees to the lower leftward of the earth-lit waning crescent Moon at about 05:00 on the morning of October 28th.

– Saturn, now shining at magnitude -0.6 above the star Antares in Scorpius starts the month setting about two hours or so after the Sun, but sets progressively earlier, to only about 90 minutes or so after the Sun at month’s end. Moreover, the planet remains within 10 degrees of the southwestern horizon during the month, which makes it very difficult to spot in less-than-ideal conditions.

– Uranus reaches its point of closest approach to the Earth on October 15th, when it will be shining at magnitude +5.71 from a distance of 2,838 million km away in the constellation Pisces. Under dark skies with no moon light, the planet might be visible to the naked eye for most of the night, but a telescope of medium aperture will be required to see the planet’s tiny greenish-grey disc between the two “fishes” of the constellation.

– Neptune is now an evening object in the constellation Aquarius, and will culminate at an elevation of 27 degrees above the southwestern horizon at a magnitude of about +7.84. Look for Neptune about two degrees to the south-westward of the +3.74 magnitude star Lambda Aquarii with binoculars, but a telescope fitted with a short focal length eyepiece is required to resolve the planet’s 2.3- arcsecond disc.

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